The evaluation of the Isolator blood culture system suggested that it is more sensitive in detecting certain bacteria, particularly yeast and staphylococci, than routine blood culture bottles. The isolator system provides quantitation of organisms in the blood, which may on occasion be useful. Since the isolator system has a higher percentage of contaminants than routine methods, it also presents a problem of interpretation of significance, particularly of low colony counts of staphylococci. A prospective study was thus initiated to blindly evaluate patients' clinical condition; these results were then correlated with any organisms isolated and colony counts obtained.